With the rapid growth of data services, there is increasing pressure on data transmission on licensed carriers. Therefore, sharing data traffic of licensed carriers on unlicensed carriers becomes an important development trend of subsequent LTE. An unlicensed carrier has the following features.
1. An unlicensed spectrum does not need to be paid, and the spectrum resource is at zero cost, therefore, it has a free/low-cost feature.
2. Individuals, businesses can participate in the deployment, and equipment vendors can deploy any equipment, therefore, it has low access requirements and low cost features.
3. An unlicensed frequency band covers available 5 GHz, 2.4 GHz and other bands, therefore, it has a large available bandwidth feature.
4. An unlicensed carrier has a resource sharing feature. That is, when multiple different systems are operating or different operators in the same system are operating on the unlicensed carrier, some ways of sharing resources may be considered to improve the spectral efficiency.
5. An unlicensed carrier has a feature of accommodating various wireless access technologies, that is, accommodating different communication standards with complex collaboration and diverse network topologies.
6. An unlicensed carrier has a feature of covering a huge number of wireless access sites, that is, has a large number of users with complex collaboration and high overhead for centralized management.
7. An unlicensed carrier has a feature of applying to many applications, that is, many services are mentioned to be operable on the unlicensed carrier, such as machine to machine (referred to as M2M) and vehicle to vehicle (referred to as V2V).
Based on the above requirements, the version LTE Rel-13 finally started its project research in September 2014. One of the important topics is that LTE systems work on unlicensed carriers. This technology will enable the LTE system to use the existing unlicensed carriers and greatly enhance the potential spectrum resources of the LTE system such that the LTE system can achieve lower spectrum cost.
Currently, the method for accessing on an unlicensed carrier is called Licensed-Assisted Access (LAA for short). For the LAA uplink, the uplink function should at least ensure that the uplink can operate normally. The basic functions of uplink include: uplink LBT process before data transmission, SRS process used for measuring uplink channel, PRACH process and the like. The PRACH process is used to acquire a Timing Advance (TA) value, request an uplink resource and acquire a transmission power. During the PRACH process, the Preamble code is sent to inform a base station that there is a random access request and enable the base station to estimate the transmission delay between the base station and the UE, such that the base station calibrates the uplink timing and sends the calibration information to the UE through timing advance signaling. For uplink data transmission on an unlicensed carrier, as the Preamble is not transmitted on the UE side, the uplink signals of different UEs in the same cell may not reach the base station at the same time, which may cause serious intra-cell interference problem.
With respect to the problem that the uplink data transmission on the unlicensed carrier may cause intra-cell interference in the related art, no effective solution has been proposed yet.
This section provides background information related to the present invention which is not necessarily prior art.